October 2012

ORBCOMM OG2 falls back to Earth after Falcon 9 Engine failure

The ORBCOMM Second Generation Satellite that was delivered to a lower-than-planned Orbit by the Falcon 9 Rocket that launched the Dragon CRS-1 Mission to ISS, has re-entered the atmosphere on Wednesday. Due to an engine failure on the first stage of the Falcon 9, the ascent profile was adjusted to deliver the primary payload (Dragon) to its required orbit with Orbcomm, being the secondary payload, drawing the short straw as the second stage of the Falcon 9 did not pass an in-flight test that prevented it from firing again to raise its altitude for Orbcomm Deployment. During first stage flight, at T+79 seconds, right when the vehicle passed Mach 1 and came up on Maximum Dynamic Pressure, a relatively violent event was visible on the business end of the Falcon 9’s first stage. There was a structural failure of an engine component that caused a rapid loss of pressure and on-board computers immediately triggered an emergency shutdown of the engine. The remaining engines of the first stage burned longer in response to the issue with Falcon 9's computers generating a modified mission profile to reach the desired orbital velocity. The second stage also burned slightly longer than planned to make up for lost performance on the first stage. Dragon was delivered to Orbit in its desired trajectory and the second stage was planned to continue the flight. "As a result of shutting down one of its nine engines early shortly after the launch, the Falcon 9 rocket used slightly more fuel and oxygen to reach the target orbit for Dragon," SpaceX said in a statement. Pre-flight, the second stage was programmed to perform a series of checks to verify that its systems are in good condition and that it had enough fuel to successfully complete a second burn to reach the 750-Kilometer orbit for Orbcomm Separation.

"For the protection of the space station mission, NASA had required that a restart of the upper stage only occur if there was a very high probability (over 99 percent) of fully completing the second burn," SpaceX said. "While there was sufficient fuel on board to do so, the liquid oxygen on board was only enough to achieve a roughly 95 percent likelihood of completing the second burn, so Falcon 9 did not attempt a restart."

Photo: NASA Kennedy

This tight margin was put in place to ensure Orbcomm and the Falcon 9's upper stage would not end up in an orbit similar to that of ISS to make sure the orbiting complex is not endangered in the event of an underburn.

Falcon 9 deployed the Orbcomm Satellite in the Low Earth Insertion Orbit, which was the backup plan to provide the option of putting the vehicle through basic tests before re-entry. The prime contractor for ORBCOMM OG2 Satellites is Sierra Nevada Corporation that agreed to built 18 G2 Spacecraft for ORBCOMM. Each ORBCOMM Satellite has a mass of 155 Kilograms and is based on the SN-100A Bus featuring a deployable solar array and on-board batteries for power generation as well as a two-way communications payload. In 2013 and 2014 SpaceX is planning to launch Falcon 9 vehicles with several ORBCOMM Satellites as primary payloads to fulfill its contract.

Photo: Sierra Nevada

With Orbcomm OG2's orbital lifetime limited, Orbcomm Inc. started an effort to perform as much vehicle checkouts as possible.

"Notwithstanding the shortened life of the OG2 prototype, the OG2 program engineering teams from ORBCOMM, Sierra Nevada Corporation and Boeing made significant strides in testing various hardware components," Orbcomm said in a statement. "After telemetry and command capability was established, several critical system verifications were performed. The solar array and communications payload antenna deployments were successful, along with verifying the performance of various components of both the OG2 satellite bus and the communications payload. The OG2 satellite bus systems including power, attitude control, thermal and data handling were also tested to verify proper operation." The satellite's communications payload was also activated and put through a series of tests, showing that it was functional.

On Wednesday, October 10, the Orbcomm Satellite re-entered the atmosphere, putting an end to its short mission meeting only some of its objectives. Re-Entry occurred at 6:19 UTC +/- 2 Minutes over the Pacific Ocean, just off the coast of Canada, burning up in the atmosphere.